1. Field of the Invention
The present invention relates to methods for generating and transmitting signaling messages in wireless communication systems, and a method for scheduling based on the signaling message.
2. Description of Related Art
Wireless third generation (3G) communication systems are currently introducing technologies in order to become spectrally efficient, while supporting data services, so as to provide improved multiplexing voice and multiplexing data services, for example. These efforts have resulted in the development of the 1xEV-DO and 1xEV-DV standards, an evolution of the CDMA2000 standard from the 3GPP2 body of standards. Similarly, the Universal Mobile Telecommunication System (UMTS) standard has introduced several advanced technologies as part of the High Speed Downlink Packet Access (HSDPA) specification. An aspect in all of these enabling technologies is to ensure that any associated control information is carried in an efficient manner.
Certain advanced or enabling technologies may include scheduling, Adaptive Modulation and Coding (AMC) and Hybrid Automatic Repeat Request (HARQ) technologies. These technologies have been introduced in an effort to improve overall system capacity. In general, a scheduler, such as is present at a base station, selects a user (or mobile station) for transmission at a given time, and adaptive modulation and coding allows selection of the appropriate transport format (modulation and coding) for the current channel conditions seen by the user.
AMC technologies enable a selection of a data rate and a transmission format (i.e., modulation level and channel coding rate) that best “suits” the scheduled user's prevailing channel condition. Delays and measurement errors could result in erroneous selection of a data rate and a transmission format, which could lead to the data transmission, at the selected data rate and transmission format, being received in error. HARQ may be used to recover from such errors.
For example, suppose a block of bits (or a packet) was sent out using QPSK modulation and using a code rate of 0.5, and was received erroneously. A retransmission of that packet takes place, in general, with a new appropriate choice of modulation and may contain a few new “parity” bits from the original set of coded bits. HARQ allows combining of the original transmission with the new transmission, rather than to discard the original transmission. This may greatly improve the probability of correct decoding of the packet. The word “hybrid” in HARQ indicates that Forward Error Correction (FEC) techniques have been used in addition to ARQ techniques. HARQ combining schemes imply that retransmissions are combined with the original unsuccessful transmissions. Accordingly, HARQ helps to ensure that transmissions resulting in unsuccessful decoding, by themselves, are not wasted.
While much of the standardization to date has focused on the forward link (downlink from base station to mobile station), similar enhancements are now being considered for the reverse link. Further evolution of 3G standards include high-speed reverse link packet access (uplink from mobile station to base station). Many of the techniques used in the forward link (i.e., fast scheduling, AMC, HARQ, etc.) may also be usable on the reverse link, so as to improve data rates and system capacity, for example.
In order to enable the above-mentioned technologies, control signaling may be needed on one or both of the reverse link (mobile station to base station) and forward link (base station to mobile station). For example, reverse link data transmission from the mobile station may take place in at least the following modes: (a) a scheduled transmission mode, and (b) an autonomous transmission mode. Typically in a scheduled mode, a central entity such as the base station will decide if a mobile station is scheduled to transmit at a particular instant or not, and, therefore, requires a signaling or schedule grant message from the base station to the mobile station. Such a transfer will be hereafter referred to as a scheduled mode transmission. In (b), the mobile station can autonomously decide when to transmit data or signaling message to the base station.
A scheduled grant message transmitted by the base station to the mobile station may consist of control information such as HARQ parameters, data rate and transmission format. This forward link signaling in HSDPA may be carried over a control channel such as high-speed shared control channel, for example. This control or signaling information in the signaling messages in the forward link may be typically encoded, e.g., with turbo codes, block codes or convolutional codes.
As discussed above, in the reverse link, mobile stations may generally be thought of as being in a scheduled transmission mode or an autonomous transmission mode. In a scheduled transmission mode, the base station decides the time at which a user may transmit in the reverse link, and, additionally, may decide to set some basic rules that should be adhered to by the users, such as rules related to transmission format (e.g., transport format) used to convey data to the base station receiver. Autonomous mode transmissions, on the other hand, can be conducted by the mobile station under some guidelines laid out by the base station or a radio network controller (RNC). For efficient resource utilization, these guidelines may be periodically adjusted by the base station or the RNC through periodic and/or event-triggered forward link signaling. Such triggering events could be embodied as a change in the interference power seen by the base station or a change in the mobile's buffer status, for example.
A scheduler in the base station may also require certain reverse link information from all the mobile stations in a sector. For example, each mobile may signal forward link quality information as seen by the mobile, the buffer status at the mobile, and the mobile's pilot transmit power to the base station. Additionally, the reverse link channel quality can be estimated by the base station by using the mobile's reported pilot transmit power and measuring the mobile's received pilot channel power at the base station. The base station can use all or some of this information to determine the reverse link or forward link scheduling priority of the mobile station, as also the date rate the mobile station can support in a given frame.
Currently, for scheduled mode transmissions, a mobile station may select a data rate and transport format that is different from that commanded by the base station. Therefore, reverse link control information related to the data transmission, such as AMC and HARQ parameters, also should be signaled to the base station. These parameters, along with the buffer size status and the mobile's pilot transmit power, are currently carried on a separate, dedicated physical layer channel from the mobile station to the base station.
Using a separate, dedicated channel, such as a high-speed dedicated physical control channel (HS-DPCCH) for carrying the reverse link control information may have several drawbacks. For example, code space (bandwidth) may be wasted. Additionally, complexity may be increased because the base station has to decode one more channel. Larger overhead may be required, since a cyclic redundancy check code (CRC) and encoder tail bits are needed for a separate control channel. As the data transmission may be decoded only if the related control information is successfully decoded, high power margins may have to be used on the control channels in order to ensure reliability of the control channel information